The Puzzle of the Frugivorous Crocs

3 Minute Read

PUBLISHED July 26, 2013

Crocodylians have a carnivorous grin. Their conical teeth and crushing jaws leave little doubt of their predatory inclinations, and this impression is only reinforced by staple documentary scenes of Nile crocodiles launching themselves from the water with the aim of snagging an unwary zebra or wildebeest. Yet the fearsome Crocodylus niloticus – as well as twelve other species of crocodylian found around the world – occasionally snaffle up less meaty fare. A variety of crocodylians put their intimidating jaws to work on fruit and other vegetation; so much so that they may actually be significant players in helping plants disperse their seeds.

Wildlife Conservation Society herpetologist Steven Platt and colleagues have collated a list of fruit and seed-eating crocodylians in a new Journal of Zoology review. The evidence the zoologists compiled comes in two types. There are direct observations of crocodylians scoffing fruit and seeds, but a great deal of information – particularly for American alligators – has been extracted from dissected stomachs and feces. The trick is determining how those fruits and seeds got there.

Just because an alligator or crocodile had seeds in its stomach doesn’t mean that the animal intentionally ate fruits or nuts. An alligator might accidentally consume vegetation while trying to catch small insects or gastropods, or when swallowing stomach stones. Hard seeds might even act as gastroliths themselves, helping grind up food in the stomach. Fruits and seeds could also come from the gut contents of swallowed prey, particularly small birds and mammals.

Despite these caveats, though, there are accounts of several crocodylian species intentionally eating fruit. Captive broad-snouted caimans have been seen eating Philodendron fruit, and captive American alligators have been observed foraging on wild grape, elderberry, and various citrus fruits. (Not to mention the occasional watermelon during enrichment.) The question is whether this happens in the wild.

In the case of the frugivorous broad-snouted caimans, researchers initially speculated that the crocodylians learned or copied the strange behavior from fruit-eating reptiles kept in the same enclosure. But the review by Platt and coauthors notes that there are scattered reports of wild crocodylians consuming fruit and seeds, and through Central and South America there are even fruits nicknamed “alligator pear” and “alligator apple” because different species of caiman regularly eat them. And sometimes wild crocodylians are inadvertently fed by humans – American alligators have been captured on motion-sensitive cameras eating corn left out by automatic wildlife feeders.

Why crocodylians are eating fruits and seeds, as well as how they’re detecting the plants, is unclear. With the exception of a fruit hitting the water and the crocodylian snapping in reflex, the attraction of fruits and seeds to the carnivores is a mystery. But, contrary what was traditionally assumed about their digestive systems, crocodylians are capable of breaking down the carbohydrates, proteins, and fats in vegetable matter, so the fruit-eating by these archosaurs could be a nutritional supplement and not just a mistake or unusual behavior.

Regardless of why crocodylians are eating fruit and seeds, the digestive system of the consumers seems to treat the hard objects just like snail shell and other indigestible items. Even though crocodylian gastric fluids are highly acidic – a pH of 1.2 to 2.0, the review notes – seeds are often found intact in the stomach contents or feces of alligators and their kin. No one knows how seeds fare after being eaten away by an alligator’s gastric fluids and beaten by gastroliths, but that’s primarily because no one has thought to investigate the question. And, as the authors point out, “the defecation habits of wild crocodiles are poorly documented,” thus hampering our ability to understand whether the seeds are being deposited in spots amenable to later germination.

Assuming that at least some seeds survive the rough treatment, though, Platt and colleagues propose that crocodylians could act as toothy, armored seed dispersers. Depending on size, life stage, and species, different sorts of crocodylians have been seen to move long distances in short intervals – several American alligators traveled at least 13.4 kilometers in a single day, while a saltwater crocodile once traveled a distance of 23.3 kilometers in a day. Given the long stretches of waterways they travel, alligators, crocodiles, caimans, and gharials could transport seeds far along river systems, distributing seeds wherever they stopped to ditch their stomach contents or otherwise relieve themselves.

More is unknown than known about crocodylians and fruit. But as Platt and coauthors argue, intentional fruit-eating seems to be a widespread behavior among these knobbly, pointy-toothed archosaurs. Crocodylians can be considered “occasional frugivores.” And while they don’t seem to have discriminating tastes about the fruit and seeds they eat, crocodylians nonetheless have the ability to transport those plant parts far and wide. Beyond those facts, though, researchers need better data. “Basic information on the defecation habits of crocod[y]lians would go far toward understanding the likelihood of post-digestive seedling survival,” Platt and collaborators write, and vegetable matter found in the guts and feces of crocodylians should be studied carefully rather than being assumed to be non-food items. The case that crocodylians are significant seed dispersers is tantalizing, but there’s a great deal of dirty work left to do.